A Fast Method for the Spatial Encoding in Rotating-Frame NQR Imaging

Robert, H; Minuzzi, A.; Pusiol, D. J.

doi:10.1006/jmra.1996.0026

Cited by 19 publications

(13 citation statements)

References 4 publications

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“…(This means we are assuming ⌬/ Ӷ 1 in Eq. [2].) This is a reasonable assumption if the sample is positioned in a region close to the axis of the coil, so that the curvature of the surfaces of constant field can simply be neglected (14).…”

Section: Methodsmentioning

confidence: 98%

“…Figure 1b shows this variant of the encoding scheme, in which the second pulse is replaced by the rapid rotating-frame pulse sequence (SEXI) (2). Then, the complete 2D function F (t 1 , t 2 ), is generated by M 1 increments of the value of t 1 , and the total acquisition time is reduced to approximately M 1 times the delay between experiments.…”

Section: Methodsmentioning

confidence: 99%

“…Images of the spatial distribution of quadrupole nuclei in solids can be produced with the rotating-frame NQR imaging (NQRI) technique (1,2). The spatially resolved NQR spectroscopy method (3,4) allows one to correlate information from the spectroscopic and spatial dimensions, thus providing the distribution of local spectral properties of the quadrupole nuclei.…”

Section: Introductionmentioning

confidence: 99%

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Mapping Molecular Orientation in Solids by Rotating-Frame NQR Techniques

Casanova

Robert

Pusiol

1998

Journal of Magnetic Resonance

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Section: Methodsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mapping Molecular Orientation in Solids by Rotating-Frame NQR Techniques

Casanova

Robert

Pusiol

1998

Journal of Magnetic Resonance

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“…The quadrature-detected NQR signal is calculated as the expectation values of (, ) (Y x cos ϩ Y y sin ) for the reference phases ϭ 0 and ϭ 90°. This formalism (9,10) and several of its applications to the description of different pulse sequences have been published elsewhere (4,(11)(12)(13).…”

Section: Two-dimensional Phase-encoding Techniquementioning

confidence: 98%

“…In rotating-frame NQR (NQR) localized spectroscopy (1-3) and imaging (4,5), spatial information is encoded using radiofrequency field B 1 gradients. These encoding techniques are based on the principle that the effective B 1 field strength experienced by a nuclear spin depends on its position along the axis defined by the RF gradient.…”

Section: Introductionmentioning

confidence: 99%

Phase-Modulated Rotating-Frame NQR Techniques for Spatial Encoding

Casanova

Robert

Pusiol

1999

Journal of Magnetic Resonance

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Nuclear Quadrupole Resonance

Herreros¹,

Harbison²

2002

Characterization of Materials

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Nuclear quadrupole resonance (NQR) was once written off as a “dead” field, but has recently had a modest rebirth, and has been applied with success to several areas of materials science, most notably the high‐ T c superconductors. The name itself is a misnomer—NQR is really (NMR) at zero field. For that reason, it has many of the same disadvantages as the more familiar NMR spectroscopy e.g., poor sensitivity and complications arising from molecular dynamics, but because it does not require a superconducting magnet, NQR is generally cheaper and can be applied to a far greater number of nuclei. It is inherently noninvasive and nondestructive, and can be applied both to pure substances and to materials in situ. It is currently, for example, being used as an antiterrorist technique to screen persons and baggage for the presence of explosives, using receiver coils that are of the order of 1 m in radius. The principal disadvantage of NQR, other than sensitivity, is that, as a radiofrequency (RF) technique, it is incompatible with conducting or ferromagnetic materials; however, for the somewhat narrow range of materials to which it can be applied, NQR gives information which is otherwise unavailable. The NQR properties of a material are primarily defined by a transition frequency or set of transition frequencies, which can be used to determine two parameters—the quadrupole coupling constant, and the asymmetry parameter. These quantities are often quite characteristic of particular materials—as when they are used to detect drugs or explosives—but are also sensitive to temperature and pressure, and can therefore be used as a noninvasive probe of these properties. Moreover, by applying external spatially varying magnetic or radiofrequency fields, the NQR signal can be made position‐dependent, allowing the distribution of the NQR‐active species in the material to be imaged. Finally, the relaxation times of NQR nuclei are highly sensitive to dynamics, and so can be used as a local probe of molecular mobility. The internal structure of materials can also be imaged by x‐ray tomography and ultrasonic methods, which depend on the existence of inhomogeneities in the distribution of x‐ray absorbers, or acoustic properties, respectively. The stress and pressure dependences of the NQR frequency are generally much stronger than those of NMR imaging, and therefore NQR is a superior method for mapping the temperature or stress distribution across a sample. Such stress distributions can be determined for optically transparent material by using polarized light; for opaque material, there may be no alternative methods. This article aims to be a general and somewhat cursory review of the theory and practice of modern one‐dimensional (1D) and two‐dimensional (2D) NQR and NQR imaging.

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A Fast Method for the Spatial Encoding in Rotating-Frame NQR Imaging

Cited by 19 publications

References 4 publications

Mapping Molecular Orientation in Solids by Rotating-Frame NQR Techniques

Mapping Molecular Orientation in Solids by Rotating-Frame NQR Techniques

Phase-Modulated Rotating-Frame NQR Techniques for Spatial Encoding

Nuclear Quadrupole Resonance

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